1. Field of the Invention
The present invention relates to a processing apparatus such as an electric drill unit, and, more particularly, to a processing apparatus using a processing head such as a drill, which utilizes the pressure of fluid such as air to set the processing head at a first (advanced) position to execute a process with the processing head and to set the processing head at a second (retreated) position in a hold mode in which no processing is done.
2. Description of the Related Art
For instance, the Japanese Utility Model Publication No. 57-57857 discloses an electric drill unit as such a processing apparatus.
According to this electric drill unit, a spindle having a drill head mounted on its distal end is rotatably driven, via a drive shaft, by an electric motor, and this drill head is pressed against an object to be processed and is rotated to process this target object. In this case, the drill head can be selectively set at two positions: the first position where the drill head contacts the target object for a process and the second position where it is retreated or separated from the object to be in a hold mode in which no process is done.
The drill head is moved forward in parallel to its axis to be set at the first position and moved backward to be set at the second position, and a piston mechanism utilizing the pressure of fluid such as air is employed as means for moving the drill head between these two positions.
This piston mechanism is constituted by a cylinder and a piston which is disposed in the cylinder to be freely movable there in parallel to the axis of the cylinder and is coupled with the spindle having the drill head mounted thereon. The piston is set at the first or second position by controlling the compressed air within the cylinder, so that the drill head moving with the piston is also set at the first or second position.
In this case, the spindle and piston can be rotated together only by the mutual coupling section, so that, even with the spindle being rotated by the motor, the piston is not rotated within the cylinder.
Such an electric drill unit is often used with the drill head facing downward. In this state, when the drill head is in a working mode to contact a to-be-processed or target object, the spindle is set at the first position (or downward position in this state) and so is the piston. In the hold mode where no work is done, however, the drill head is moved upward to the second position to be separated from the target object, and the piston is also set at the upper position in this state; this upper position is maintained by the air pressure inside the cylinder.
Accordingly, when the air pressure within the cylinder to support the piston is reduced in this hold mode, the drill head section is moved downward due to the weight of the section including drill head and spindle and the tare of the piston, which may damage the unit itself and the target object as well.
As a solution to this problem, there needs some means to prevent the movement of the drill head from the second position to the first one when desired, namely, a fall preventing mechanism mounted to the piston mechanism. Such a fall preventing mechanism may be a mechanism for side-locking the piston rod, etc. by means of a small air cylinder rod or a holding mechanism for applying frictional force on the piston rod to restrict its movement. Installing such a fall preventing mechanism in the drill unit, however, complicates the overall structure of the processing apparatus and thus makes it more difficult to make the apparatus compact.